This Application relates in general to processing metals and more particularly to an apparatus and process for removing volatile coatings from scrap metal.
Because the energy required to melt aluminum metal is considerably less than that required to extract aluminum from its ores, much of the aluminum used in manufactured goods derives from aluminum scrap--and one of the principal sources of aluminum scrap is discarded beverage cans. Because the typical aluminum beverage can has an organic coating, usually a lacquer, on its interior and exterior surfaces, aluminum beverage cans tend to produce a considerable amount of dross when introduced into a melting furnace. In this regard, within the furnace the coating volatizes and ignites before the can melts, and the combustion which ensues oxidizes the aluminum, thereby creating the dross which is actually an oxide of aluminum. Processors of aluminum scrap therefore usually subject aluminum beverage cans to a delacquering operation before introducing them into a melting furnace. Also, beverage cans may contain residual moisture, perhaps in the form of the beverage itself, and to ensure the safety of those operating the melting furnace, the moisture should be eliminated before the cans enter the furnace.
The typical delacquering process attempts to subject the coated beverage cans to temperatures high enough to volatilize the coating, but not so high as to melt the aluminum. Some processes even operate at reduced oxygen levels to lessen the chances of ignition, but all current processes are difficult to control. A slight change in the moisture content can reduce the operating temperature to the point that much of the coating remains, or an increase in the mass of the cans processed may cause the system to react such that it produces excessive temperatures which ignite the coating on some of the cans.
The present invention resides in an apparatus and process which circulates heated air of reduced oxygen content past coated aluminum scrap to remove a coating from the aluminum. Even though the nature and mass of the scrap may vary, the rarefied air remains at a substantially uniform temperature somewhat below melting temperature of the aluminum, and hence the aluminum experiences little oxidation. By varying the mass flow of the rarefied air, the system compensates for variances in the content of the scrap and the mass of the scrap.